1. Field of the Invention
This invention is related to a discharge tube and in particular to one which utilizes piezoelectric material to provide required voltage for the discharge tube.
2. Description of the Prior Art
The conventional fluorescent lamp is a mercury-vapor electric-discharge lamp having the inside of the bulb or tube coated with fluorescent material so that ultraviolet radiation from the discharge is converted to light of an acceptable color. As shown in FIG. 1, the fluorescent lamp includes an elongated tube 1 which is filled with mercury-vapor and a small amount of argon and coated with fluorescent material 2 on the inner surface. Both ends of the elongated tube 1 are each provided with a filament 3 which is coated with calcium oxide or barium oxide for increasing its emission capability. The filament 3 is also used as the electrode. The elongated tube 1 is provided with two plugs 4 at two ends thereof. As the filaments at two ends of the elongated tube 1 are applied with a high voltage, the cathode will emit a large amount of electrons toward the anode and the electrons will collide with the gas atoms thereby ionizing the gas atoms and releasing a large amount of electrons. As the speed of the electrons moving toward the anode exceeds a certain value, discharge will take place, causing the mercury-vapor to emit ultraviolet light which will be converted to visible light by the fluorescent material 2.
In order to ionize the gas to discharge, a high voltage must be applied to both ends of the fluorescent lamp and so a starting device, ballast and a starter are required for supplying current to the filaments so as to emit a large amount of free electrons, producing a momentary high voltage to activate electrons to move at a high speed, and lowering the voltage applied to both ends of the fluorescent lamp and cutting off the current supplying thereto when discharge takes place. For causing the filaments to emit a large amount of electrons, the filaments must be sufficiently heated and so the filaments must be supplied with current by a push-button device or a starting device. A higher voltage is required to speed up electrons and ionize mercury molecules when starting, and the discharge can be maintained by a lower voltage. A ballast is usually used for accomplishing the demands of voltage variations in starting and use.
However, the conventional fluorescent lamp cannot convert all of the electric energy into visible light and a relatively large amount of the electric energy is converted into heat thereby lowering the efficiency to 05.-0.6. In addition, after having used for a certain period of time, the emission substance will be all consumed and both ends of the fluorescent lamp will be blackened thereby ending the service life of the fluorescent lamp.